1. Field of the Invention
This invention relates to substituted polybenzimidazole articles. In particular, this invention relates to processes for the production of substituted polybenzimidazole articles by reacting a pyrocarbonate with an unsubstituted polybenzimidazole polymer.
2. Prior Art
Polybenzimidazoles are a well known class of polymers characterized by a high degree of thermal stability and resistance to chemical reaction. As a result polybenzimidazoles have found application in a wise variety of end uses. For example, polybenzimidazole fibers are useful as insulating materials that do not give off toxic fumes when heated. Such fibers are particularly suited for use where high temperature resistance is important. Polybenzimidazoles have also been used as membranes, ultrafilters, reverse osmosis devices and for other separatory functions.
While polybenzimidazole products are generally resistant to chemical reaction, they are sometimes subject to attach at the imidazole nitrogen-hydrogen bond by strong acids. To limit their susceptibility to chemical reaction and improve their performance, polybenzimidazole polymers can be chemically modified. For example, the crosslinking of polybenzimidazole polymers, as described in U.S. Pat. Nos. 4,020,142 and 4,154,919, increases their resistance to chemical attack by removing the reactive nitrogen-hydrogen bond on the imidazole ring.
In another effort to prevent chemical reaction at the imidazole nitrogen-hydrogen bond, substituted polybenzimidazole polymers have been prepared. For example, U.S. Pat. No. 4,377,546 discloses a substituted polybenzimidazole which is part of a polymeric alloy wherein the hydrogen on the imidazole nitrogen has been replaced by a phenyl group.
U.S. Pat. No. 3,578,644 discloses the substitution of an hydroxyl substituent onto a polybenzimidazole polymer by the reaction of a polybenzimidazole polymer with an omega-haloalkanol or a 1,2-alkylene oxide. The reaction requires the presence of a basic catalyst and an organic salt is formed as a by-product. In addition, because of the use of gaseous alkylene oxide, a pressurized reaction container is necessary as the reaction vessel. Further, the halo-alkanol reaction does not produce an hydroxyl substitution on some types of polybenzimidazole polymers, such as poly-2,2-(m-phenylene)-5-,5'-bibenzimdiazole and other similar polybenzimidazoles because of steric hindrance between the reactive imidazole rings. See also U.S. Pat. No. 4,599,388, for another hydroxyl substituted polybenzimidazole polymer.
U.S. Pat. No. 3,943,125 discloses various substituted polybenzimidazole polymers, which are produced by the reaction of substituted tetramino pyridines or their acid salts with a suitable acid halide or dianhydride. The resulting precyclized intermediates are cyclodehydrated and crosslinked to produce various substituted polybenzimidazole polymers. However, the percentage of substituted polybenzimidazole polymers produced by this reaction ranges only between about 20 and 40 percent of the available polybenzimidazole polymer. Further, although the '125 patent broadly discloses a large number of substituted tetramino compounds, it fails to specifically describe them. In addition, the process for preparation of these substituted polybenzimidazole polymers is significantly different from the process of the instant invention.
U.S. Pat. No. 3,518,234 discloses a process for the preparation of N-aryl substituted polybenzimidazole polymers by cyclodehydrating the precursor compounds with an acidic substance, such as polyphosphoric acid or p-toluenesulfonic acid. However, the substituted polybenzimidazole polymer produced is not obtained by direct reaction with a polybenzimidazole polymer and substantial heating of the reaction vessel is necessary to achieve the desired end product. See also U.S. Pat. No. 4.579,915.
It is therefore an object of this invention to produce novel aryl and alkyl substituted polybenzimidazole polymers.
It is an additional object of this invention to produce aryl and alkyl substituted polybenzimidazole polymers using an unsubstituted polybenzimidazole polymer as the precursor material.
It is a further object of this invention to produce aryl and alkyl substituted polybenzimidazoles wherein the substitution is substantially complete.
It is a still further object of the present invention to produce substituted polybenzimidazole products which show a high degree of resistance to chemical attack and which are stable at high temperatures.
These and other objects as well as the scope, nature and utilization of this invention will be apparent to those skilled in the art from the following detailed description and appended claims.